1. Field of the Invention
The present invention relates generally to a semiconductor structure and process thereof, and more specifically to a semiconductor structure and process thereof, which includes a resistor structure having two U-shaped metal layers located at the two sides of a dielectric material.
2. Description of the Prior Art
In a semiconductor process, polysilicon is often used in forming resistors capable of providing high resistance. These resistors can be used in place of load transistors. When load transistors of a static random access memory (SRAM) is replaced by polysilicon resistors, the number of transistors in the SRAM can be lowered which reduce costs and enhance the integration ratio of the SRAM.
The steps of forming resistor structures by polysilicon may include covering a silicon nitride layer on a reserved polysilicon area to define a location of a polysilicon resistor by exposing a polysilicon area to remove. Then, the polysilicon of the reserved polysilicon area is removed by methods such as etching processes, so that contact holes for forming contact plugs of interconnects to electrically connect polysilicon resistors with wires are formed in the reserved polysilicon area.
But said process still has a few drawbacks. For instance, a height difference between the reserved polysilicon area and other areas can arise after the etching process is performed because of the covering of the silicon nitride layer on the reserved polysilicon area. The height difference can lead to an incomplete polishing process of metals used to fill the contact holes for forming the contact plugs, and the some metal may remain outside of the contact holes. Besides, the polysilicon of the polysilicon area to remove is hard to be removed by etching processes. For example, the polysilicon of the polysilicon area to remove will be over-etched when only a dry etching process is performed, which can damage the structures below the polysilicon. The polysilicon of the reserved polysilicon area covered by the silicon nitride layer will be etched through as the polysilicon of the polysilicon area to remove is etched by a dry etching process coupled with a wet etching process, due to the wet etching process being an anisotropic etching process. As a result, holes will be hard to fill with metals, which affecting the performances of polysilicon resistors.